Function new_columns_for_join_on 

fn new_columns_for_join_on(
    hash_join_on: &[&PhysicalExprRef],
    projection_exprs: &[(Column, String)],
    column_index_offset: usize,
) -> Option<Vec<PhysicalExprRef>>

This function generates a new set of columns to be used in a hash join operation based on a set of equi-join conditions (hash_join_on) and a list of projection expressions (projection_exprs).

Notes: Column indices in the projection expressions are based on the join schema, whereas the join on expressions are based on the join child schema. column_index_offset represents the offset between them.